Meteo France weather.  Le Mans 24 Hours 8th-14th June 2015. Circuit de la Sarthe, Le Mans, France.

Guy, the engineer from Météo France, is a weather specialist dedicated to the TOYOTA GAZOO Racing team at the Le Mans 24 Hours but also at most World Endurance Championship events. He explains his role in the team.

Why do you need weather forecast during a race?

“Motorsport is very sensitive to weather changes so the need for greater accuracy in short-term forecasting is real. Météo France provides TOYOTA with support in forecasting all the weather events which may occur during a test session or especially during a race. Depending on their evolution, weather events can affect the race strategy and the car set-up. This is a key factor, for example in the choice of the tyre type. The global strategy chosen by the team may depend on the weather conditions and in case of bad choices, the race result can be negatively affected. Unlike at a tennis tournament where it is impossible to play in the rain, on a circuit the drivers continue to race but rain has a massive influence on car handling.”

How do you work with the team especially for the Le Mans 24 Hours?

“To be able to best anticipate the testing and the race strategies, I start to follow the weather forecasts 15 days before the start of the race week. We must ask the right questions, such as are we in a warm weather period or in a cold weather period, what are we able to predict 15 days before? Will it be unusually hot or unusually cold, will it rain or will it remain dry? Gradually, as we approach the deadline, we will know if it will rain during the first part of the race or during the second, and then gradually we will be able to say that it will rain in three minutes at Mulsanne. We try to be as precise as possible closer and closer to the event.”

To reach this level of precision, what tools do you use?

“We use specific Météo France models, ie numerical simulations of the state of the atmosphere, especially with temperature and humidity parameters. For long-term forecasts we run twice a day on these models. On a long-term period, it is not possible to know whether it will rain during the first hour of the race but only to define if this day will be in a dry period, or not. Gradually, as one gets closer to the event, the simulation models will turn six to eight times a day and will be more precise, to the nearest hour. As far as we approach the real weather, we will have a look at what the satellite is able to see, and what the different Météo France radars located throughout the country are able to show. Within a hundred kilometers, our forecasts depend on the radar we set up ourselves close to the circuit for the exclusive use of TOYOTA. This device allows us to have a one hundred meters resolution, every minute. It is just like zooming in on a photo. But there is also another parameter that nothing can replace, this is human expertise. A numerical simulation will never be as reliable as what I can see in real time, putting my head out of the window.”

What is a typical day for you?

“I’m always one of the first of the team to arrive on the circuit to provide the engineers with the first newsletter of forecasts upon their arrival. Based on this information, they should be able to update their strategy and/or their test program. If there is a qualifying session, they must be able to consider the range of potential lap times. During the practice sessions and the race the update is made continuously.”

How do you organize during the 24-hour race?

“During this very particular race, we are two people so we can work without any interruption. Specifically, I arrive on the previous Saturday at 7.00am and gradually as we get closer to the event we are more and more busy. Every hour, the information is more and more precise. We are located in one of the team trucks in the paddock, but we go frequently in the garage to “take the temperature”. We live intensively each race and we fully share the good and bad times with the team. For a weather engineer this is a very original way to wor